[R] setAs between a new S4 class and "POSIXlt"

[Christoph Buser]

Dear R gurus

I've a question concerning the transformation of a new S4 class
(that I defined) and the existing class "POSIXlt". I did the
following: 

## Definition of the new class:
setClass("dtime",
         representation(data = "POSIXlt"),
         prototype(data = as.POSIXlt("2004/06/01")))

## Transformation between the new class "dtime" and "POSIXlt":
setAs("dtime", "POSIXlt", def = function(from) {
  from at data
})
setAs("POSIXlt", "dtime", def = function(from) {
  new("dtime", data = from)
})

## Create a new "dtime" object:
(x1 <- new("dtime"))
str(x1)
## Transformation to "POSIXlt" class works well:
(y1 <- as(x1, "POSIXlt"))
str(y1)

## Transformation to "dtime" class fails
as(y2, "dtime")
> Fehler in insertMethod(methods, sig, args, def, TRUE) : 
	inserting method into non-methods-list object (class "NULL")

## This works properly
new("dtime", data = y2)

####################################################################

## Now I put another setAs for the Subclass "POSIXt"
setAs("POSIXt", "dtime", def = function(from) {
  new("dtime", data = from)
})

## and the transformation to "dtime" class works:
as(y2, "dtime")


I tried to understand what happend, without success. Could
someone give me a hint or a reference (some help page or others) 
to improve my understanding, please?
Thank you very much.

I work with:

platform i686-pc-linux-gnu           
arch     i686                        
os       linux-gnu                   
system   i686, linux-gnu             
status   Under development (unstable)
major    2                           
minor    1.0                         
year     2005                        
month    03                          
day      22                          
language R                           


Regards,

Christoph Buser

--------------------------------------------------------------
Christoph Buser <buser at stat.math.ethz.ch>
Seminar fuer Statistik, LEO C11
ETH (Federal Inst. Technology)	8092 Zurich	 SWITZERLAND
phone: x-41-1-632-5414		fax: 632-1228
http://stat.ethz.ch/~buser/